Alternative to AC? Scientists test old tech to cool a room

WSU

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Cooling is important. Especially in dry and humid climates. But the air conditioners in our homes, offices, and cars are responsible for approximately 1,950 million tons of carbon dioxide emissions annually, or the equivalent of 3.94% of global greenhouse gas emissions.

In order to find a sustainable solution and alternative to ACs, Washington State University (WSU) researchers are experimenting with a 60-square-foot chamber to test out ancient cooling methods.

“Cooling is increasingly in demand in buildings, especially as the climate gets hotter,” said Al-Hassawi, assistant professor in WSU’s School of Design and Construction, in a press release. “There might be inclusion of mechanical systems, but how can we cool buildings to begin with — before relying on the mechanical systems?”

The researchers aren’t using electricity but passive systems that use wind towers for water evaporation to cool down temperatures.

The test chamber, which looks very much like a huge ship container, is solar-powered with battery storage and doesn’t require any grid power. The chamber can be heated to a temperature between 125 and 130 degrees Fahrenheit (52 and 54 degrees Celcius) in a bid to test out the cooling effect of the system.

The passive downdraft cooling system has been tested under the hot, dry conditions of Phoenix, Arizona.

“We can simulate extreme conditions,” said Al-Hassawi. “With smaller scale models, we can also do much quicker tests and get results sooner than having to wait on large-scale prototype construction.”

It’s a concerning issue. Of the figure of 1,950 million tons of carbon dioxide emissions annually due to ACs, 531 million tons come from energy expended to control the temperature and 599 million tons from removing humidity.

“There’s a lot of new construction with the rising global population that is going to happen in the coming years, and a lot of it is going to be in the developing world,” Al-Hassawi said.

“So if we build like we’ve been building and continue to rely on mechanical systems to meet cooling demands, that’s going to be an issue. There’s going to be a lot more air conditioning that’s needed, especially with the population rise in the hotter regions of the world,” he added.

Passive cooling systems go back to about 2500 BC in ancient Egypt. The strategy used for cooling involves capturing breezes using wind towers. In hot areas, the moisture is evaporated, which in turn cools the air. The cooled air becomes heavy and sinks by gravity into a living space below.

“It’s an older technology, but there’s been an attempt to innovate and use a mix of new and existing technologies to improve performance and the cooling capacity of these systems,” he said. “That’s why research like this would really help,” he said. “How can we address building design, revive some of these more ancient strategies, and include them in contemporary building construction? The test chamber becomes a platform to do this.”

The researchers hope that as the Earth continues to become hotter, ACs will be replaced by these passive system designs.

The study was published in Energies.

Study abstract:

Energy demand for active mechanical space cooling is projected to double by 2050. Wider adoption of passive cooling systems can help reduce demand. However, familiarity with these systems remains low, and innovation in the field is constrained due to a lack of cost-effective, accessible performance evaluation methods. This paper reports the design, construction, and commissioning of an affordable, self-contained environmental test chamber. The novel chamber replicates a range of outdoor conditions common in hot, dry regions, making possible year-round testing of reduced-scale prototypes. Data from calibration testing are reported, showing no significant difference in evaporative efficiency when a reduced-scale prototype tested in the chamber is compared with datasets from prior full-scale testing. Analyzing the results using an independent sample two-tailed t-test with a 95% confidence interval found a p-value of 0.75. While measured outlet air velocities for reduced-scale and full-scale prototypes differed to some extent (root mean square error of 0.45 m/s), results were nevertheless deemed comparable due to errors introduced by the rapid change in wind speeds and directions at full scale. Future chamber modifications will correct misalignments between data collected from the two scales and prevent observed increases in the chamber’s relative humidity levels during testing.